Field of the Invention
The invention relates to a method for diagnosing an activation of a swirl control valve, in particular for diagnosing a swirl control valve adjustment device which outputs a position signal that indicates the position of the swirl control valve.
In internal combustion engines, a so-called swirl control valve is frequently used to control the charging of a cylinder with mixture. This swirl control valve is located downstream of the air collector before the inlet valve and influences the flow-in conditions of the intake air, for example in that one of two inlet ducts of a cylinder is closed to a greater or lesser degree. As a result, it is possible to influence the swirl with which the aspirated gas passes into the cylinder. Hence the name xe2x80x9cswirl control valve.xe2x80x9d Each cylinder has its own swirl control valve; the swirl control valves are connected by way of a coupling linkage which is actuated by an adjustment device which simultaneously outputs a position feedback signal, so that a control device has information on the current position of the swirl control valves. One reason for which this is necessary is that many of the characteristic diagrams used in modern internal combustion engines for control also take into account the position of the swirl control valve.
It is therefore necessary to check the function of the actuation of the swirl control valve, not least because it is a component which affects emissions and which is legally required to be subject to continuous checking during the operation of an internal combustion engine.
Hitherto, in order to check a swirl control valve, it has been customary to provide a second, i.e. redundant, sensor which senses the position of the swirl control valve so that correct functioning of the actuation of the swirl control valve and in particular the activity of the adjustment device and the position signal of the position feedback can be checked. See, for example, U.S. Pat. No. 6,135,085 or the corresponding German patent application DE 198 60 323 A1. Such redundancy is, however, costly, in particular because a separate sensor on each swirl control valve is needed to monitor the coupling linkage.
Japanese published patent application JP 08074583 A discloses a method for diagnosing a swirl control valve which is seated downstream of a throttle valve in the intake tract of an internal combustion engine, in which method, after the swirl control valve has been adjusted, the degree of opening of the swirl control valve is sensed directly or indirectly, for example by means of a pressure sensor downstream of the swirl control valve, the pressure signal which is obtained here is compared with a stored setpoint value and a defect in the swirl control valve is diagnosed on the basis of this comparison. This publication does not specify under which operating conditions this diagnosis is to be carried out.
It is accordingly an object of the invention to provide a method for diagnosing an activation of a swirl control valve, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which does away with the requirement for redundant position sensors.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of diagnosing an activation of a swirl control valve disposed downstream of a throttle valve in an intake tract of an internal combustion engine. The method comprises:
actuating the swirl control valve by a predefined adjustment travel within a supercritical operating range of an intake pipe pressure in the intake tract downstream of the throttle valve during lambda-1-controlled operation of the internal combustion engine; and
if a specific step-like change in pressure dependent on the adjustment travel does not take place in the intake tract downstream of the throttle valve, diagnosing a defect in the activation of the throttle valve.
In accordance with a specific embodiment, the following steps are carried out to diagnose an adjustment device that activates the swirl control valve and outputs a position signal indicating a position of the swirl control valve:
adjusting the swirl control valve by an adjustment travel until the position signal indicates a specific limit position;
sensing the intake pipe pressure between the swirl control valve and the throttle valve before and after the adjustment;
determining a difference between the intake pipe pressure sensed before and after the adjustment; and
diagnosing a defect in the adjustment device for different drops below a specific threshold value.
The invention is based on the recognition that an adjustment operation of the swirl control valve leads to a specific change in the intake pipe pressure in a quite specific operating range of the intake pipe pressure of an internal combustion engine. If the swirl control valve is adjusted by a specific adjustment travel, for example as far as a specific limit position, a specific jump in intake pipe pressure occurs. The adjustment of the swirl control valve continues to have no effect on the load of the internal combustion engine if it is in the supercritical operating range of the intake pipe pressure because the sucked-in air mass flow rate is then independent of the adjustment of the swirl control valve.
According to the invention, the adjustment of the swirl control valve therefore takes place only at supercritical intake pipe pressure. The expression xe2x80x9csupercriticalxe2x80x9d range is a term of art known to those of skill in the art. The pressure goes supercritical when the intake pipe pressure downstream of the throttle valve is less than approximately 55% of the ambient pressure. If the pressure is in this supercritical range, adjustment of the throttle valve does not lead to a jump in the load.
If the jump in the intake pipe pressure does not occur when there is an adjustment of the swirl control valve, either the adjustment mechanism or the position feedback is faulty. The method according to the invention thus easily permits diagnosis of the actuation of the swirl control valve by means of measuring pickups which are present in any casexe2x80x94the intake pipe pressure is usually sensed in an internal combustion engine.
The method according to the invention has, in particular, the advantage that measuring errors which are included in both pressure measurements, i.e. in the intake pipe pressure measurement, are eliminated by the formation of differences.
The diagnostic results are particularly reliable, of course, if the jump in pressure is large. For this purpose it is possible, within the supercritical range, to delimit a particular range in which the jump in pressure is particularly large. It is also possible to use a swirl control valve adjustment travel which is as large as possible, because the jump in intake pipe pressure depends on the adjustment travel of the swirl control valve which takes place during the actuation.
In accordance with an added development of this advantageous refinement, it is possible firstly to determine the current position of the swirl control valve before a swirl control valve adjustment operation which is intended for a diagnosis and then to select the specific limit position provided for in the diagnosis adjustment in such a way that a maximum adjustment travel results from the current position.
Further improvement in the diagnosis is obtained by virtue of the fact that it is carried out repeatedly in succession. Because a quite specific swirl control valve position is generally desired for a specific operating phase of an internal combustion engine, double execution of the diagnosis can be particularly preferably achieved if, in the first instance, the adjustment from the setpoint position predefined by the control device into a specific limit position is utilized for a first diagnosis and then the adjustment back into the setpoint position is utilized for a second diagnosis. In this way, two advantages are achieved, on the one hand precisely the setpoint position desired by the control device for the swirl control valve is maintained with the exception of the time period of the diagnosis, and on the other hand two diametrically opposed swirl control valve adjustments which can be used for a diagnosis are carried out.
Of course, it is desired to let diagnoses run basically as imperceptibly as possible. For this reason, it is particularly preferred if a diagnosis utilizes signals or adjustments which occur during normal operation. For this reason, it is particularly preferred to allow the adjustment of the swirl control valve which is necessary for the diagnosis to coincide with a swirl control valve activation which is requested in any case during operation of the internal combustion engine. This permits a swirl control valve adjustment travel which is necessary in any case to be utilized for the diagnosis, the diagnosis being carried out in one advantageous development only if a specific minimum adjustment travel is reached. In one refinement of this development which uses normal operating conditions of the swirl control valve, an adjustment of the swirl control valve which is requested by the control device during normal operation of the internal combustion engine can also be utilized by suitably enlarging the adjustment travel actually requested, in such a way that a specific suitable minimum adjustment travel is reached if the adjustment travel which is actually requested by the control device is not sufficient for reliable diagnosis. In this development, the swirl control valve is therefore adjusted beyond a limit position requested during normal operation until the minimum adjustment travel necessary for the diagnosis is reached.
Alternatively, a minimum adjustment travel which is necessary for the diagnosis can also be ensured by triggering the diagnosis only if the swirl control valve is located within a specific range near to its minimum or maximum degree of opening. This can be detected, for example, from the position signal. If the swirl control valve is then actuated away from this minimum or maximum degree of opening in the direction of the opposite limit position, a maximum adjustment travel, and thus a maximum jump in pressure in the intake pipe, are obtained.
Other features and modes of the method that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for diagnosing the adjustment device of a swirl control valve, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.